This invention relates to an improved system for testing the transmit/receive modules of a phased-array antenna apparatus.
Phased-array antennas are used in, for example, radar systems since they can scan wide areas while remaining stationary. A phased-array antenna includes an array of antenna elements, each having its own transmit/receive module for transmitting and receiving signals via the antenna element. Each transmit/receive module includes a phase shifter. The total antenna beam is steered by controlling the phase shifts in the transmit/receive modules.
To confirm normal operation of a phased-array antenna, it is necessary to test the receive circuits of the individual transmit/receive modules. A prior scheme for such testing equips each transmit/receive module with a receive check circuit that diverts part of the unamplified transmit signal from the transmit section of the module to the receive section of the same module. During normal operation, the receive check circuit is switched off, so that the transmit signal is not diverted into the receive section. During a test, the receive check circuit is switched on and the part of the unamplified transmit signal diverted into the receive section is used as a test signal.
A problem with this scheme is that the receive check circuits themselves may malfunction. If the switch in the receive check circuit becomes stuck in the on-state, for example, then during normal operation, part of the amplified receive signal will be fed back via the receive check circuit thereby into the receive circuit, setting up an oscillation. Even one of the transmit/receive modules oscillating in this way can seriously distort the total received signal power, thereby causing the antenna array to fail as a whole.